Subsections

• HydrogeologicMapping Leveling Procedure
• HydrogeologicMapping Well Measurement Procedure
• HydrogeologicMapping Field Procedures

HydrogeologicMapping Activities

We will make use of a topographic base map (Fig. 6.1) to map an approximation of the water table at the Heard Museum.

Figure 6.1: Heard Museum topographic map. Sample points are labeled by number and name (see Table ).

In order to do this, we will collect water elevation data, by measuring the height of surface and groundwater occurrences relative to known elevation benchmarks. The method is summarized in Fig. 6.2 and a form for field notes is provided in Table 6.1. Given these point elevations, and assuming that the water table roughly parallels the ground surface, we will construct a contour map of the water table.

Figure 6.2: Field procedure for measuring elevation difference from a known point using a sighting level. Note our feet will stay dry, so $Z_o>Z$ and therefore $h>I$.

HydrogeologicMapping Leveling Procedure

To carry out a leveling survey (see Fig. 6.2 for meaning of symbols):

1. select an instrument man (person doing the sighting)
2. measure eye-height $I$ using stadia rod held close to the instrument man
3. instrument man stands on a benchmark (point of known elevation $Z_o$)
4. rod man places base of stadia rod at location where ground elevation $Z$ is sought
5. instrument man reads elevation on stadia rod, holding sight level so that level bubble is centered on line in viewfinder, $h$ is the position of the viewfinder line on the stadia rod
6. For elevation differences greater than height of rod, or distances too far to read stadia rod with hand level
   1. surveyor determines $Z$ at an intermendiate location
   2. then moves to that location and repeats these steps as needed.
   3. In this case the formula for elevation $Z$ becomes: $Z =\ Z_o + (I - h)_1 + (I - h)_2 + ...$.
   4. Remember to record $I$ and $h$ for each of these ``turnaround'' points (see extra lines in Table 6.1)

HydrogeologicMapping Well Measurement Procedure

When wells are available, the water table elevation is measured by determining the elevation of the ground at the well (``collar elevation''), and subtracting the depth to water measured by beeper tape.

1. determine the elevation of the ground adjacent to the well ($Z_o$)
2. if a well housing is present, measure the height of this ($H$)
3. measure the depth to water from the top of the well housing ($D$)
4. water table elevation $Z = Z_0 + H - D$

Table 6.1: Field data form for leveling survey. All values in feet, water elevation $Z = Z_o + (I - h)$.

Station	Station	Benchmark	Eye	Rod	Water
#	Name	Elev ($Z_o$)	Height (I)	Reading (h)	Elev. (Z)
1	Hand-dug Well	593
2	Bullfrog Pond	548
3	Stagnant Pond	533
4	Mallard Marsh Lagoon	528
5	Woodduck Lagoon	528
6	Upper Wilson Creek	528
7	Canoe Trail	525
8	Windmill	525
9	Lower Wilson Creek	525

Proceed through the points in numerical order, see Fig. 6.3 for help in navigating the route.

Figure 6.3: Satellite image of Heard Museum, with sample locations. Location numbers are upright when photo is oriented with north up.

HydrogeologicMapping Field Procedures

1. Gather at site of new Science Center (north of Heard Museum Visitor Center). In the center of the traffic circle is Point 1 (Fig. 6.1).
2. Assemble your team and make a site reconnaissance using the material handed to you

3. First observation will be done at the hand-dug well (Point 1, Fig. 6.1), in the parking lot. Use the Well Measurement procedure (section 6.1.2).

4. Go to next points (2, 3, 4, ...on the map) and evaluate the surface water level using the hand-leveling technique shown in Fig. 6.2
5. Record all the values in the data table Table 6.1.
6. Measure the groundwater level at the point Wind Mill well using the beeper tape.
   1. Determine the elevation of the base of the concrete housing of the well using the leveling technique
   2. Determine water table elevation using the Well Measurement procedure (section 6.1.2)